1. Field of the Invention
This invention relates to a method for joining a diamond to a metal and to the article of manufacture produced by such a method. The article of manufacture is useful as a tool such as a machine tool or a microtome blade.
2. Discussion of the Prior Art
It is well known that metals do not generally provide satisfactoy junctions to diamonds. This is primarily due to the fact that in the fluid state, most metals do not wet the diamond, or wet it inadequately, so that an adhesive joint is difficult to form. There are exceptions to this. In particular, a satisfactoy method of joining diamonds to metal is described in U.S. Pat. No. 3,192,620 which issued to Huizing et al on July 6, 1965. Huizing et al discovered that a very satisfactory adhesive junction between a diamond and a metal can be obtained by using as a solder an alloy of gold containing at least 1 percent by weight of tantalum and/or niobium. The alloy disclosed in Huizing et al is the alloy used in the present invention.
For many purposes, however, the knowledge that a strong bond between a metal and diamond can be formed using this particular alloy is not enough to allow one to make useful articles of manufacture in a commercially feasible fashion. For example, the temperature at which the alloy melts is near or above the graphitization temperature of diamond, depending on the alloy composition. To achieve best results, then, the alloy must be heated very rapidly to its melt temperature and then cooled very rapidly. Induction heating is a common way, and in fact the preferred way, of achieving rapid heating. It has been observed that during the heating step, particularly heating by induction, the diamond will move unless it is held in place. Even with clamping, some rotation of the diamond may occur. This means that if one wishes to orient a particular surface of the diamond relative to a particular surface of the metal shank, some means must be provided to prevent movement of the diamond.
In addition to this, when the shank and the diamond are to be ground to produce an exposed, sharp cutting edge on the diamond, a particularly effective bond must be achieved between all opposed surfaces of the diamond and the metal shank. If not, the vibrations which occur during the grinding step will cause fractures or cleavages to appear in the diamond either during or after manufacture and therefore ruin the cutting ability of the diamond edge.